Wavelength division multiplexer and wavelength division multiplexing system

Abstract

A wavelength division multiplexer comprising three WDM optical fiber couplers connected in a tree-like configuration. Two multiplexed wavelengths λ 2 and λ 4 inputted through a common port are split and outputted separately via two branch ports. Wavelengths λ 1 and λ 3 inputted via two different branch ports are combined and outputted via the common port. The wavelengths λ 1, λ2, λ3, and λ 4 are set sequentially larger. Isolation between neighboring channels (wavelengths) is low, but isolation between one channel and the channel adjacent to the neighboring channel is sufficiently large. By transmitting light of neighboring channels in opposite directions on the same optical fiber, leakage of the optical signal does not occur even with a low isolation between neighboring channels.

What is claimed is:  
     
         1 . A wavelength division multiplexer comprising a single common port and three or more branch ports such that light received via the common port is split into at least three optical signals of different wavelengths that are transferred to corresponding branch ports, wherein an isolation α between a first wavelength and a second wavelength adjacent to the first wavelength is set to 10-17 dB and an isolation β between the first wavelength and a third wavelength adjacent to the second wavelength is set to 20 dB or greater.  
     
     
         2 . A wavelength division multiplexer as recited in  claim 1 , wherein the value of β is set to 20-40 dB.  
     
     
         3 . A wavelength division multiplexer as recited in  claim 1 , further comprising a plurality of WDM optical fiber couplers connected in a tree-like structure.  
     
     
         4 . A wavelength division multiplexer comprising a thin film filter type three-port device and WDM optical fiber coupler connected in tandem.  
     
     
         5 . A wavelength division multiplexer comprising a thin film filter type three-port device and a WDM optical fiber coupler, wherein one of branch ports of the three-port device is connected to a common port of the WDM optical fiber coupler.  
     
     
         6 . A wavelength division multiplexer as recited in  claim 5 , wherein one or more other thin film filter type three-port devices are connected to the thin film filter type three-port device connected to the WDM optical fiber coupler, such that a branch port of one thin film filter type three-port device is connected to a common port of another thin film filter type three-port device.  
     
     
         7 . A wavelength division multiplexer as recited in  claim 5 , wherein the thin film filter type three-port devices separate received optical signals into wavelengths, while the WDM optical fiber coupler multiplexes optical signals for transmission.  
     
     
         8 . A wavelength division multiplexer comprising a first thin film filter type three-port device for separating received light into optical signals of a short wavelength band and optical signals of a long wavelength band, and two wavelength division multiplexer units; 
 the common port of each wavelength division multiplexer units being connected to a corresponding branch port of the first thin film filter type three-port device; and    each of the two wavelength division multiplexer units comprising a second thin film filter type three-port device and a WDM optical fiber coupler, wherein one of branch ports of the second three-port device is connected to a common port of the WDM optical fiber coupler.    
     
     
         9 . A wavelength division multiplexer comprising a thin film filter type three-port device for separating received light into optical signals of a short wavelength band and optical signals of a long wavelength band, and two wavelength WDM optical fiber couplers, wherein the common port of each WDM optical fiber coupler is connected to a branch port of the thin film filter type three-port device.  
     
     
         10 . A wavelength division multiplexing system employing one or more wavelength division multiplexers and configured to perform bi-directional communications over a single optical fiber, while using opposite transmission directions for neighboring wavelengths, 
 each of the wavelength division multiplexers A wavelength division multiplexer comprising a single common port and three or more branch ports such that light received via the common port is split into at least three optical signals of different wavelengths that are transferred to corresponding branch ports, wherein an isolation α between a first wavelength and a second wavelength adjacent to the first wavelength is set to 10-17 dB and an isolation β between the first wavelength and a third wavelength adjacent to the second wavelength is set to 20 dB or greater.    
     
     
         11 . A wavelength division multiplexing system employing one or more wavelength division multiplexers and configured to perform bi-directional communications over a single optical fiber, while using opposite transmission directions for neighboring wavelengths, 
 each of the wavelength division multiplexers comprising a thin film filter type three-port device and WDM optical fiber coupler connected in tandem..    
     
     
         12 . A wavelength division multiplexing system employing one or more wavelength division multiplexers and configured to perform bi-directional communications over a single optical fiber, while using opposite transmission directions for neighboring wavelengths, 
 each of the wavelength division multiplexers comprising a thin film filter type three-port device and a WDM optical fiber coupler, wherein one of branch ports of the three-port device is connected to a common port of the WDM optical fiber coupler.    
     
     
         13 . A wavelength division multiplexing system employing one or more wavelength division multiplexers and configured to perform bi-directional communications over a single optical fiber, while using opposite transmission directions for neighboring wavelengths, 
 each of the wavelength division multiplexers comprising a first thin film filter type three-port device for separating received light into optical signals of a short wavelength band and optical signals of a long wavelength band, and two wavelength division multiplexer units,    the common port of each wavelength division multiplexer units being connected to a corresponding branch port of the first thin film filter type three-port device, and    each of the two wavelength division multiplexer units comprising a second thin film filter type three-port device and a WDM optical fiber coupler, wherein one of branch ports of the second three-port device is connected to a common port of the WDM optical fiber coupler.    
     
     
         14 . A wavelength division multiplexing system employing one or more wavelength division multiplexers and configured to perform bi-directional communications over a single optical fiber, while using opposite transmission directions for neighboring wavelengths, 
 each of the wavelength division multiplexers comprising a thin film filter type three-port device for separating received light into optical signals of a short wavelength band and optical signals of a long wavelength band, and two wavelength WDM optical fiber couplers, wherein the common port of each WDM optical fiber coupler is connected to a branch port of the thin film filter type three-port device.